Conventionally, in the field of powder metallurgy, in case of filling a raw material powder in a mold and warm press-molding a formed body, in order to improve a flowing property of the raw material powder at a time of filling the raw material powder in the mold and to improve a pressing property of the formed body by increasing a lubricating property between raw material powders and between the raw material powder and the mold at a time of press-molding the formed body, a warm molding raw material powder formed by mixing the raw material powder with lithium stearate as a lubricant is generally used as a raw material in the powder metallurgy. However, in a case where the lithium stearate is mixed, although a melting point of the lithium stearate is about 220° C., there is a problem in that, if the raw material powder is heated at a temperature of 150° C. or more, the flowing property of the raw material powder deteriorates. In addition, there is a problem in that sufficient lubricating and pressing properties cannot be obtained by using the lithium stearate.
As disclosed in Japanese Unexamined Patent Application Publication No. 2000-27350, it is known that the flowing property of the raw material powder can be improved by adding a small amount of fatty acid metallic salt having an average particle diameter of 4 μm. However, the lubricating property at the time of press-molding cannot be obtained by adding such a small amount of the fatty acid metallic salt. In addition, generally, if an amount of the fatty acid metallic salts suitable to obtain the flowing property is added, the flowing property is lowered. In addition, since production cost of the fatty acid metallic salt having a very small particle diameter is higher than that of a general fatty acid metallic salt, there is a problem in that the fatty acid metallic salt having such a very small particle diameter is uneconomical.
In addition, as disclosed in Japanese Unexamined Patent Application Publication No. 2001-294902, there is proposed a technique of using a lubricant containing components having a low melting point below a press-molding temperature. However, if the lubricant containing the low melting point lubricating component is heated at a temperature exceeding the warm molding temperature, there is a problem in that the flowing property of the raw material powder cannot be obtained.